refactor: use $$restProps API

- add ref prop for applicable components (#196)
- add slot to Content Switcher `Switch` component (#183)
- remove fillArray, css utilities

src/components/ListBox/ListBoxMenu.svelte

@@ -1,10 +1,5 @@
 <script>
-  let className = undefined;
-  export { className as class };
-  export let id = Math.random();
-  export let style = undefined;
-
-  import { cx } from '../../lib';
+  export let id = "ccs-" + Math.random().toString(36);
 
   $: menuId = `menu-${id}`;
 </script>
@@ -12,9 +7,7 @@
 <div
   role="listbox"
   id={menuId}
-  aria-labelledby={$$props['aria-labelledby']}
-  aria-label={$$props['aria-label']}
-  class={cx('--list-box__menu', className)}
-  {style}>
+  class:bx--list-box__menu={true}
+  {...$$restProps}>
   <slot />
 </div>